Opc update rate

Four 4 tags are communicated over OPC UA, a boolean, an integer bit , a string value 7 characters , and a floating point value. In the controller program, the boolean value cycleson and off every ms. At the same interval, the string text "rotates" in the following manner:.

All 4 tags are visible to the client. However, the tags only update every 9 or 10 seconds. In the HMI application, I have the boolean tag and the string configured to update every ms, but this is not occurring. The other two number tags remain unchanged since they are not programmed to but are configured to refresh every 2 seconds in the HMI client.

This client seems to have no problem seeing the tags update at the actual rate the changes occur in the controller, so I guess the problem is in the WinCC Advanced application. The value in the cache is updated whenever the server reads from the device. The server reads values from the device at the update rate specified by the dagroup object's UpdateRate property, and only when the item and group are both active. In addition, for analog type data data with the additional OPC Foundation Recommended Properties 'High EU' and 'Low EU' the percentage change between the cached value and the device value must exceed the DeadbandPercent property specified for that item in order for the cached value to be updated.

Quality — The Quality of the server item is a character vector that represents information about how well the cache value matches the device value.

The Quality is made up of two parts: a major quality, which can be 'Good' , 'Bad' , or 'Uncertain' , and a minor quality, which describes the reason for the major quality. The Quality of the server item can change without the Value changing. For instance, if the OPC server attempts to obtain a Value from the device but that operation fails, the Quality will be set to 'Bad'.

You must always examine the Quality of an item before using the Value property of that item. TimeStamp — The TimeStamp of a server item represents the most recent time that the server assessed that the device set the Value and Quality properties of that server item.

The TimeStamp can change without the Value changing. For example, if the OPC server obtains a value from the device that is the same as the current Value , the TimeStamp property will still be updated, even if the Value property is not.

The toolbox uses these three mechanisms in various ways to return data from those functions, to provide event information, to update properties of toolbox objects, and to log data to memory and disk.

OPC Data Returned from a Data Change Event describes the data change event notification mechanism used with subscribed, active groups, with the refresh function, and by the toolbox logging process.

You initiate a synchronous read operation by using the read function. When you read from a dagroup object, all items in that group are read in one instruction. You can specify the source of a synchronous read operation as 'cache' or 'device'. If you read from the cache, the server simply returns the value in the cache.

The default is -1, which specifies that the sampling interval is the same as the publishing interval of the subscription. By default this value is 0. The meaning of this parameter depends on the deadband type selected.

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With the act of writing values, do you notice if the values come in faster? If not, then there might be a DCOM or network configuration issue. If so, there might be a problem with your client. Turn those on and see what is the time the writes actually occur and what time the reads actually take place.